1. Field of the Invention
The present invention relates to a bicycle used for cross-country, particularly an improved crank gearwheel assembly for providing a variable speed arrangement for such a bicycle.
2. Description of Prior Art
As known, a variety of bicycles are continuously proposed in compliance with different demands in the present bicycle industry. Especially in bicycling for cross-country, it is hard to maintain a more light and speedy feature of the bicycle body under the consideration of safety.
A crank gearwheel assembly used in a conventional bicycle, as shown in FIG. 1, generally includes a crank body 1A of which a top end integrally forms a coupling portion 4A. The coupling portion 4A is further configured with five retentive claws 41A to which larger diameter and smaller diameter gearwheels 5A, 6A together are secured thereto. In manufacture, the gearwheels of different diameters 5A, 6A are separately fabricated by a lathe process and then screwed to the five retentive claws 41A. Through a stamping process, it often occurs that some burrs appear on the gearwheels 5A, 6A resulting in an inadequate quality and inaccurate assembly. Additionally, due to separate fabrication of the gearwheels 5A, 6A, the gearwheels 5A, 6A may have inconsistent fit tolerances with regard to the crank body 1A when both of the gearwheels 5A, 6A are respectively screwed to the crank body 1A. Accordingly, an angular deviation may appear between the screwed gearwheels 5A, 6A resulting in an inaccurate action of a derailleur system used in conjunction with the crank gearwheel assembly. Therefore, it is understood that such a crank gearwheel assembly basically lacks economic effectiveness and usefulness.
Recently, although some bicycles utilize the feature of separately fabricating the crank body 1A and the coupling portion 4A to constitute two independent structures, thereby achieving a better quality in manufacture, the crank body 1A is still formed as a solid construction and also screwed together with the coupling portion 4A. Not only may the above-mentioned problem not be resolved, but also another problem of weighting the whole bicycle results.